Compositions of calcium carbonate, process for the production and uses of the same



March 12, 1968 EIZO YASUI ETAL 3,373,34

COMPOSITIONS OF CALCIUM CARBONATE, PROCESS FOR THE PRODUCTION AND USES OF' THE SAME Filed Aug. 15, 1964 2 Sheets-Sheet 1 H/RosHl YAMADA March 12, 1968 EIZO YAsul ETAL 3,373,134

COMPOSITIONS 0F CALCUM CARBONATE, PROCESS FOR THE PRODUCTION AND USES 0F THE SAME Filed Aug. 13, 1964 2 Sheets-Sheet 2 ya -c yew NVENTORS: EIZO YASUI SHICHIRO SHODA HIROSHI SUZUKI HIROSHI YAMADA United States Patent O 3,373,134 CMPUSTIONS 0F CALCIUM CARBONATE, PROCESS FOR THE PRDUCTIGN AND USES GF THE SAME Eizo Yasui, Shichiro Shoda, Hiroshi Suzuki, and Hiroshi Yamada, Nagoya-shi, Japan, assignors to Toa Gosei Kagalru Kogyo Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Aug. 13, 1964, Ser. No. 389,453 Claims priority, application Japan, Gct. 18, 1963, 38/54,917; May 7, 1964, 39/25,527 6 Claims. (Cl. 260-415) ABSTRACT F THE DISCLUSURE Calcium carbonate crystals of the vaterite and aragonite type containing silicic acid for use as a reinforcing ller in a vulcanization composition, and a process for the preparation thereof.

This invention relates to a new nely divided and a light composition of calcium carbonate in which amorphous silicic acid is dispersed Within the grains of calcium carbonate, to a process for the production of such compositions and to vulcanizable compositions of synthetic rubber comprising one of said calcium carbonate cornpositions.

An object of the invention is to provide a new iinely divided and light composition of calcium carbonate suitable for use as ller which is demanded in the manufacture of rubber, paper and various plastics. A further object is to develop the uses of the new compositions for the invention.

Calcium carbonate nds wide applications in the manufacture of rubber, paper, plastics, paints, foodstuffs, cosmetics and medicines etc. However, the crystalline structure, distribution of grain size, apparent density, dispersibility and surface activity of the calcium carbonate used should vary depending on the purposes to which it is applied.

The crystalline structure of calcium carbonate includes three types of modifications, namely the calcite type (hexagonal system) which is seen in the calcite and egg shell; the aragonite type (rhombic system) which is seen in the aragonite and scallop shell; and the vaterite type (pseudohexagonal system) which is found in an unstable intermediate state.

Among them, the calcite type crystalline calcium carbonate is most stable, and the aragonite type crystalline calcium carbonate as well as the vaterite type crystalline calcium carbonate are said to ultimately convert into the calcite type by themselves.

To obtain nely divided calcium carbonate, naturally occurring lime stone is usually ground in a mill. However, the finely divided calcium carbonate obtained in this way is usually of the `calcite type and shows non-uniform grain size, an apparent density of at least 0.6 and lower dispersibility, and additionally contains many impurities. Therefore it is unsuitable for use as a ller in the manufacture of rubber, paper, etc., as mentioned above. In addition, finely divided calcium carbonate may also be produced by other synthetic methods, one of which is carried out by blowing gaseous carbon dioxide obtained from the calcination of lime stone into `a purified milk of slaked lime. A further method of producing the iinely divided calcium carbonate Iconsists of the reaction of calcium chloride with sodium carbonate in an aqueous reaction medium. However, all of the crystalline calcium carbonate obtained by the prior `art methods are in the form of coarser crystals of the calcite type. Calcium carbonate ICC containing a large proportion of the aragonite or vaterite type crystals has been said to be very diicult to produce. U.S. Patent No. 805,581 discloses that crystalline calcium carbonate of the aragonite type may be produced by blowing gaseous carbon dioxide .and ammonia gas into an aqueous solution of calcium chloride. lt has been found, however, that the `calcium carbonate product obtained by the method of this patent contains `a predominant proportion of the calcite type crystals and less than 50% of the aragonite type. Furthermore, these crystals have a very large grain size and lower dispersibility. The grain size and apparent density of the product cannot be controlled by this method. It is also known that crystalline calcium carbonate of the vaterite type may be formed by decomposing basic calcium carbonate in the presence of certain ions (refer to BulL Chem. Soc. Japan 35, 1937, 1962). It is also known, that calcium carbonate having a large proportion of vaterite type crystals can not be prepared by commercial process because of its instability and would probably need an extremely large amount of energy under special conditions to prepare.

Thus, all of the prior art methods ot producing crystalline calcium carbonate are exclusively directed to the production of the calcite type of crystalline calcium carbonate. A process for the commercial production of the vaterite and aragonite type crystalline calcium carbonates has not been developed. From the view-point of the crystalline structure, the vaterite and aragonite type crystalline calcium carbonates appear to have a greater surfaceactivity than the calcite type and show various advantages in the aforesaid applications if they may be obtained in a pure, stable and iinely divided state. It has been found that nely divided and lighter -calcium carbonate may be obtained when gaseous carbon dioxide or ammonium carbonate is reacted with calcium chloride in an aqueous solution which is kept alkaline at pH value of 8 or higher by addition of ammonium hydroxide, and in the presence of an amount of colloidal silicic acid. The calcium carbonate product obtained in this way is in the form of composition in which amorphous .silicic acid is dispersed within the grains of calcium carbonate.

According to an aspect of the invention, we provide a process for the production of finely divided lighter compositions of calcium carbonate in which amorphous silicic acid is dispersed in the `grains of calcium carbonate, characterized in that a carbonation reagent selected from the group consisting of gaseous carbon dioxide and ammonium carbonate is reacted in the presence of colloidal silicic acid with calcium `chloride in an Iaqueous solution which has been made alkaline at a pH value of 8 or higher by addition of ammonium hydroxide, while the pH value of the reaction mixture is maintained at 8 or higher during the reaction by addition of ammonium hydroxide.

In the process of this invention, the resulting product is iinely divided and shows a grain size of up to several microns and, if desired, of from l micron to several lmillimicrons. It is not dicult to produce the product of an apparent density of only 0.3 or below by the process of the invention. As to the crystalline structure of calcium carbonate present in the compositions produced by the process of the invention, it is seen that the calcium carbonate may be of the vaterite type crystals or of the aragonite type crystals or of a mixture thereof together with a small proportion of the calcite type crystals. In the compositions the grains of calcium carbonate are tine, lighter in weight and contain amorphous silicic acid dispersed therein, so that they show little tendency to be involved in secondary aggregation. In this respect, the compositions produced by the process of the invention are distinct from a mixture of calcium carbonate grains and iine particles as'zaisfi of amorphous silicic acid in which the particles of the silicic acid exist outside the grains of calcium carbonate. In the compositions produced by the process of the invention, the silicic acid is present in the form or amorphous acid and not in the form of crystalline calcium silicate. This cankbe conrmed from X-ray diftractometry of the compositions which gives diffraction charts of amorphous silicic acid and crystalline calcium carbonate of the aragonite type and/ or the vaterite type.

The reason why calcium carbonate present in the compositions is in the form of line crystals is probably because the colloidal silicic acid Auniformly dispersed in the liquid medium constitutes the nucleus for the crystallisation of calcium carbonate. In order to obtain iinely divided crystalline calcium carbonate, it is necessary to provide the presence of colloidal silicio acid in the reaction medium wherein calcium carbonate is Vbeing formed, in an amount suliicient to insure that the resulting crystals of calcium carbonate may contain at least 2% of silicic acid. With a lower amount of the collodial silicic acid, the resulting calcium carbonate may be in the-form of crystals of the aragonite or vaterite type and in the form of coarser crystals of a size of from several microns to ten microns or more. On the other hand, the presence of an excess of colloidal silicic acid is not preferred, because the crystals resulting from the carbonation reaction can lose the original nature of calcium carbonate itself. It is preferred to provide thepresence of 'colloidal silicic acid in said reaction medium in an amount up to about 200% by weight of calcium carbonate formed. Y

The colloidal silicic acid used in the process of the invention may be prepared from the decomposition of a water-soluble silicate such as sodium silicate with acid. We have further found that, in the process of the invention, the presence of colloidal silicic acid also may be provided in situ in the reaction medium by decomposing an aqueous solution of a water-soluble silicate with an aqueous alkaline solution of calcium Vchloride containing ammonium hydroxide or with an aqueous solution of ammonium carbonate. When the reaction medium containing the colloidal silicic acid prepared in situ is milky, the process of the invention may be carried out without dith- 'According to an embodiment of the invention, when gaseous carbon dioxide is used -as the carbonation reagent, the process may be carried out in such a way that an aqueous solution of a water-soluble silicate is mixed with van alkaline aqueous solution of-calcium chloride containing ammonium hydroxide. The resulting reaction mixture containing the `colloidal silicic acid is reacted with gaseous carbon dioxide while the reaction mixture is maintained yalkaline at a pH value of 8 or higher during the reaction by addition of ammonium hydroxide.

According to a further embodiment of the process of the invention, when ammonium carbonate is used las the carbonation reagent, the process may be carrier out in such a way that an aqueous solution of a water-soluble silicate (e.g. sodium silicate) is mixed with an aqueous solution of ammonium carbonate and the resulting reaction mixture containing the colloidal silicic acid is reacted with an aqueous solution of calcium chloride while the reaction mixture is maintained alkaline at a pH value of 8 or higher during the reaction by addition of ammonium hydroxide. In order to obtain finely divided compositions of calcium carbonate, however, it is preferred to ernploy sodium silicate in which the ratio of SiO2/Na2O, namely the content of the silicic acid is higher.

In the process of the invention, it is essential that the pH value of the reaction mixture or zone where calcium carbonate is being formed is maintained constantly at 8 or higher and preferably at 8.4 or above during the reaction by addition of ammonium hydroxide. Below a pH value of 8, the resulting lcrystals contain a predominant proportion of Vthe calcite type crystalline calcium carbonate. In particular, below a pH value of 7, the resulting crystals consist entirely of the calcite type of calcium carbonate. In order to keep the reaction mixture constantly at a pH value of S or higher, the reaction mixture mayv bonation reagent. In View of the purity of the calcium car- Y bonate formed, it is preferred to use gaseous carbon dioxide, as the use of ammonium carbonate often results in the formation of the calcite type crystalline calcium carbonate unless the reaction conditions are strictly controlled. It is to be noted that an alkali metal carbonate such as sodium carbonate and potassium carbonate can- Vnot be employed as the carbonation reagent in the process of the invention. If an Valkali metal carbonate is used as the carbonation reagent, the calcium carbonate formed is then entirely in the form'of the calcite'type crystals and there is not obtained any finely divided and lighter composition of vaterite and aragonite type crystalline calcium carbonates.

In the process of the invention, the carbon dioxide used Y as'the carbonationreagent may be in the form of aconcentrated gas. However, it is preferred to employ the carbon dioxide which has been diluted with an inert gas such as nitrogen, since the formation land growth of crystalline calcium carbonate may be more easilycontrolled.

In case the process of the invention is carried out using either gaseous carbon dioxide or ammonium carbonate as the carbonation reagent, it is preferred to agitate'thereaction mixture vigorously by means of a strong agitator and perform the reaction under such conditions 'that high mixing takes place'in the mixture. Particularly when the carbonation reaction is'elected using gaseous carbon dioxide, rapid introduction of the carbon dioxide is'likely to result ina zone wherethe gastand-Iiquid-when` contacted'with each other becomesl neutral or acidic, Vthough the nature of the whole reaction mixture 'is --apparently maintained alkaline. For this reason, it is desirable toY agitate the mixture carefully.

In the process of the invention, generally when the'ca'r-V bonation reaction is effected at a temperature of 35 C.v or

Yabove the resulting-calcium carbonate is substantially in the form of the aragonite type crystals, and when the carbonation reaction is at a temperature lower than 35 C., the Vresulting calcium 4carbonate is substantiallyiin the form of the vaterite type crystals. In order to yform a crystalline calcium carbonate in whichV theprop'ortion of the aragonite type crystals is higher or predominant, itis preferred to carry out the reaction at a temperature of 40 C. or above. In order to form a crystalline calcium carbonate in which the proportion ofthe'vaterite'type crystals is higher, it is preferred to bring 'about thereaction at a temperature of 20 C. or below.

It is acknowledged that there are some methods of the prior art which are similarl to but distinct1 from the process of the invention (refer to German YPatent No. 1,156,919).

These methods consist of adding an amount of sodium comparative examples. According to themethods of the prior art, it is impossible to obtain aragonite and Vaterite Ytype crystalline calcium carbonate having a -high surface activity.

In general, the line crystals of calcium carbonate of a grain size of up to l micron are likely to aggregateinto lumps and show a higher vapparent density due to-their secondary coagulation, unless they art treated in a certain manner. The finely divided compositions of calcium carbonate produced by the process of the invention do not show a tendency to aggregate without such a special treatment. The fine grains of calcium carbonate in the compositions show a decreased degree of coagulation and a better dispersibility, as the amount of the amorphous silicic acid present therein is increased.

X-ray diffractometry of the composition of the invention shows diffraction of both of the vaterite type crystalline calcium carbonate and of amorphous silicic acid. Electron microscopic observation shows that it is difficult to distinguish the fact that the crystalline calcium carbonate and the aqueous silicic acid constitute separate individual grains (refer to PG. 1). From the electron microscopic observation, it is assumed that the individual grains are substantially composed of calcium carbonate and diat the amorphous silicic acid is in the form of fine particles dispersed within the grains. However, this assumption is difficult to confirm. Nevertheless, the aforesaid new composition produced by the process of the invention is a uniform composition of the vaterite type crystalline calcium carbonate and amorphous silicic acid and distinguishable from such a mixture or compositions in which the grains of the vaterite type calcium carbonate are so mixed with fine particles of amorphous silicic acid that the latter exist around and outside the former. In the new composition, the grains are present in the form of spherulite and contacted with each other in a similar way to the structure of carbon black. We have found that this new uniform composition of the vaterite type crystalline calcium carbonate and amorphous silicic acid is excellent as a whitecolored and reinforcing filler for synthetic rubbers.

According to a further aspect of the invention, therefore, we provide a new uniform composition of the amorphous silicic acid containing vaterite type crystalline calcium carbonate of which X-ray diffractometry shows diffraction of both the vaterite type crystalline calcium carbonate and of amorphous silicic acid, and in which electron microscopic observation cannot distinguish that the calcium carbonate and the silicic acid constitute individually separate grains.

It is known that unlike natural rubbers, synthetic rubbers themselves are of lower strength and that only when added with a reinforcing filler so as to relieve the concentration strain do they show improved tensile strength and improved elongation. Hitherto, carbon black is commonly used 'as black-colored reinforcing filler for synthetic rubbers but it cannot be used yfor the production of rubber products of white or other color. For the latter purposes, White carbon may be used as the filler. However, when white carbon is incorporated into synthetic rubbers, the tensile strength may be improved but the elongation is decreased and hardness is increased. The upper limit of the quantity of white car-bon which may be incorporated is only 80 parts by weight per 100 parts of the rubber. Further, there have been produced various fillers by treating finely divided calcium carbonate with a surface active agent to improve its dispersibility, by activating finely divided calcium carbonate by incorporating therein a substance which may react with the synthetic rubber during the subsequent vulcanization, or by applying colloidal silicic acid or calcium silicate onto the surfaces of finely divided calcium carbonate. However, such fillers substantially consisting of nely divided calcium carbonate are suitable only for imparting improved elongation and hardness to Synthetic rubbers and are not effective to improve tensile strength and tear strength of synthetic rubbers. Besides, such fillers are effective only for limited kinds of synthetic rubbers, particularly, steric synthetic rubbers. In order to reinforce synthetic rubbers, it is common to enhance the ability of the synthetic rubbers to be reinforced by blending with natural rubbers or to incorporate both white carbon and finely divided calcium carbonate into synthetic rubbers. However, these procedures do not give entirely satisfactory results. We have now found that the uniform composition of amorphous silicic acid and the vaterite type crystalline calcium carbonate has excellent properties as a reinforcing filler of white color for synthetic rubbers. As stated previously, the amount of amorphous silicic acid present in the uniform composition of the invention may vary from 2% to 200% by Weight of the crystalline calcium carbonate. If the amount of silicic acid is less than 2% by weight of calcium carbonate, the grains of the vaterite type crystalline calcium carbonate can be coarser and show a decreased ability to reinforce synthetic rubbers. On the other hand, if the amount of silicic acid is more than 200% by weight, the composition has properties similar to white carbon and loses its filler effect. The reinforcement effect of the composition of the invention for synthetic rubbers is particularly better when the grains of the calcium carbonate present therein have an average grain size not more than 0.1 micron and preferably not more than 0.05 micron. The uniform composition of amorphous silicic acid and the vaterite type calcium carbonate according to the invention, even if not subjected to any special surface treatment, can impart to synthetic rubbers higher tensile strength, higher tear strength, proper modulus elongation, proper hardness and other favourable properties as not attainable by using finely divided crystalline calcium carbonate of the calcite and aragonite types.

With the conventional surface treated and finely divided calcium carbonate filler, the reinforcing effect of this filler usually varies depending on the kind of surface treating agent used, so that there is a tendency for the filler to be effective for only a limited group of rubbers. The uniform composition of amorphous silicic acid and the vaterite type crystalline calcium carbonate of the invention has a reinforcing effect for all kinds of synthetic rubbers, particularly steric synthetic rubbers. In general, as the amount of filler incorporated into rubber is increased, the filled rubber product shows reduced workability, decreased strength and decreased elongation, so that the rubbery nature of the product is considerably impaired. Even when the filler of the present invention is incorporated into synthetic rubbers in large amounts such as 160 parts by weight per parts of the rubbers, and into steric synthetic rubbers in an amount of 100 parts by weight per 100 parts of rubber, the strength of the rubber product is rather likely to increase and the modulus as well a-s the tear strength increase without considerable loss of the elongation and without extreme increase in hardness. Even if the amount of the ller of the present invention incorporated is greatly increased, the rubbery nature of the product deteriorates only slightly, but the reinforcing effect is enhanced. These favourable characteristics of the filler of the present invention are neither shown by other white colored fillers of similar kinds nor by a mixture which is prepared merely by mixing fine particles of silicic acid with ordinary finely divided calcium carbonate. Although it is not clear why the reinforcing effect of the filler of the present invention is excellent and unique as stated above, it may be assumed that the higher surface activity of the vaterite type crystalline calcium carbonate plays a great part. It is to be noted, however, that the filler of the present invention does not give very favourable results yfor reinforcing natural rubbers. A reason therefore is probably that the filler of the invention causes a num-ber of breakdowns in the molecules of natural rubbers and promotes the gelation of natural rubbers in the course of the mastic'ation step in a similar way to other reinforcing fillers such as white carbon.

Vulcanization of synthetic rubbers comprising the uniform composition of amorphous silicic acid and the vaterite type crystalline calcium carbonate according to the invention may -be carried out in any conventional manner with or Without addition of various vulcanization acids or additives. In case it is desired to complete the valcanization in a shorter period of time, the time of vulcasilicio acid. The resulting comparative product has'- such nization required may be properly controlled by adding a properties as shown also in Table 1.

TABLE 1 Reaction condition and prop- In the presence ci colloidal silicio In the absence of colloidal silicio acid erties of product acid (thei nvention) (comparative) Y Reaction temperature, in C 40 20 50 40- 20. Apparent density. 0.46 48 0.50. 1,00 0.85. Crystalline structure Araannife Vetcnte Aragonite.-. Vaterite Vaterite, Grain size range, inmicrons 1-1.5 1- -3 1 12 Shape of crystals Fine columnar Spherical Columuar- Spherica1 Spherical.

X-ray didraction chart of the une columnar crystalsis shown in FIG. 2 of the attached drawings. NolEf-The crystalline structure and grain size range are determined by X-ray diraction and by Velec tron microscope, respectively.

proper amount of vulcanization promotor such as, for Y For the above Table 1, it is seen that the difference example, di-ethylene glycol, cyclohexyl amine etc. Y between the presence and the absence of colloidal silicic The synthetic rubber products so vulcanized show by acid in the solution of calcium chloride results in arethemselves higher tensile strength, higher modulus and mar-liable diterence in the grain size and other properties higher tear strength than such synthetic rubber products of the resultant products.

which'have'been obtained using any of `the commercial 20 Exampl'e'z reinforcing llers of white color. They further show a properly improved elongation without greater hardness A11 eieCtfO-magnetiauy Stiffed aUtOCiWe 0f a Capacity Vand show good extending effect and rohbei-yrnatnie, of 3 l. is charged with 2 1. of an aqueous solution of 5% With reference to the attached drawings, Fi@ 1 shows of calcium chloride which has been obtained by double a diagynmniatioalrrvisw of the grains of oaloinni oai-bondecomposition of slaked lime with ammonium chloride ate present in the Compositions produced ,by the :process and WhCh has Contained 27111018. Of aIIlIIlOAlllllm hydroxide of the invention,V per mol. of the calcium chlorideras well as colloidal FIGS. 2 and 3 show charts of X-ray diffraction of SiiiCiC acid iD an 2tiiOUIlt 0f 2% by Weight 0f the two samples of the Compositions produced by the proooss calcium chloride. Nitrogen gas is introduced into the reof the invention actor to a pressure of 3 lig/cm?, and the charge is then The invention is now illustrated with reference t kept at temperatures aS SPeCiiied ill Table 2 'belOW and Vexamples and comparative examples which are nonlinnim agitated at a stirrer speed of.6r00` revolutionsl per minute. tivo to the scope of tho invention ,and in which the Under stirring, carbon dioxide gas is blown into the quantity of ammonium hydroxide used is given in molar Vcharge under partial pressure of 0.2kg./cm.2. The carbonpoi moL of Voaloinm chloride present, the pressure in 35 ation reaction takes place and is then continued luntil kga/cm.2 (absolute), and parts and percent are given the pH value of the reaction mixture has reached "8.6. lhy weight Subsequently the reaction product deposited is removed VIn those examples, analysis of the ofystalline sti-nonno from the Areactor and washed with water until it is of calcium carbonate formed is performed according to free fiom the ChiOfide iOIlS- The PlOdl-Ct iS then dried the method described in the Anal Chem. 2o, 886-889, 40 at 100 C. for 3 hours to give a wmposition of amorphous 1948, silicic acid and crystalline calcium carbonate -which has Example 1 such properties as shown in Table 2 below. For comparison, theabove procedure is repeated similarly inthe An autoclave of a capacity of 5 l, and provided with absence of colloidal silicic acid to vgive the comparative .an electromagnetic stirrer is charged with 3 l. of an-aque- 45 products of which properties are also shown in Table 2.V

TABLE 2 Reaction conditiol and properties of In the presence of silicio acid (the invention) In the absence of silicio acid (comparative) pro u Reaction temperature in C. 35 18 50 35 18 `Apparent density 0. 50. 0.65 0.52 0.89

Crystalline structure Aragonite Aragonlte-i-Calcite Vaterite agonite Vaterite G rsjn size range, in crous 1-2 1-0.5 (Ar.) 2-3 (Ca1.)---- Less than 0.1.-.. 2-4 s1o --2-3. Snape of crystals Colulrlrmln.y -Spherulite Columuar Spherical Spherical.

ous solution of 10% of calcium chloride which addilIt is also vseen that the dilerence between the presence tionally has contained 2 mols. of ammonium hydroxide of colloidal silicic acid and the absence of the same reper mol. of the calcium chloride as well as colloidal silicic .sults in a remarkable difference in the crystalline and acid in an amount of 10% by weight of the calcium chlograin size range of the products obtained. ride. Nitrogen gas is then introduced into the autoclave y In the above Examples l and 2, the colloidal silicio to apressure of 5 kg./cm.2. The charge is kept at various acid in'the aqueous solution of calcium chloride has been temperatures as specilied 1n Table 1 below and agitated provided by reacting the calcium chloride solution conat a stirrer speed of 500 revolutions ,per minute. Carbon taining ammonium hydroxide with an aqueous solution dioxide gas is then blown into the chargeunderthe partial of such asodium silicate which contains 33% of SiOZ vpressure of 0.3 lig/cm.2 and under stirring. The carbonand has a SiOn/NagO'molar ratio of 2.6. Y

ation reaction takes place immediately and thereafter is continued until the pH valve of the reaction mixture has Example 3 reached 8.4. After the reaction is completed, the result- VAn electro-'magnetically stirred autoclave of a capacity ing product deposited is removed from the reactor Vand of 301. is charged with l5 l. of an aqueous solutionof 7% washedwith rwater until rit is free from the chloride ions. of calcium chloride which has'been obtained by double de- The product is subsequently dried at 100 C. for 3 hours composition of .slaked lime with .ammonium chloride to give a composition of amorphous silicic acid and andwhich has contained 2mols. of ammonium hydroxide crystalline calcium carbonate which has such properties per mol. of the calcium chloride. To the chargeare as shown in Table l below. For comparison, the above slowly added under stirring 1.21 kg. of such a sodium vprocedure is repeated similarly inthe absence of colloidal silicate which has a Si02 content of 32.6% and Va of 2.5 and in which colloidal silicic acid is present in a CaCl2/Si02 molar ratio of 1.1. Nitrogen gas is introduced into the reactor to a pressure of 3 kga/cm?, and the charge is kept at 8 C. and agitated at a stirrer speed of 750 pressure of kg./cm.2, and the charge is vkept at a tem- 5 revolutions per minute. Carbon dioxide gas is then blown perature of 10 C. and agitated at a stirrer speed of 500 into the charge under stirring and under a partial presrevolutions per minute. Carbon dioxide gas is blown into sure of 0.1 kg./cm.2. The carbonation reaction takes place the charge under stirring and under a partial pressure of and is continued until the pH value of the reaction mix- 0.2 kg./cm.2. The carbonation reaction takes place and is ture has reached 8.4. After the reaction is completed the continued until the pH value of the reaction mixture has 10 reaction product deposited is removed from the reactor, reached 8.2. After the reaction is completed the reaction filtered on Buchner funnel under suction and dried at product deposited is removed from the reactor and washed 100 C. for 5 hours. There is obtained in a yield of 85% with distilled water until it is free from the chloride a nely divided and White colored composition of an ions. The product is subsequently dried at 105 C. for apparent density of 0.39 gJcc. and of good dispersibility hours in a dried and then ground to give very much 15 in which the amorphous silicic acid is uniformly disiinely divided white powder of an apparent density of persed in the grains of the vaterite type crystalline calcium 0.35 g./cc. in a yield of 92%. X-ray diffraction of this carbonate. product shows that this product consists of amorphous Exam le 6 silicic acid and the vaterite type crystalline calcium carbonp ate, as will -be seen from the X-ray diirraction chart of 20 An aqueous solution of ammonium carbonate is added FIG. 3. As stated above, electron microscopic observation with sodium silicate having a SiO2/Na20 molar ratio of shows that it is diliicult to distinguish the fact that the 2.55 to form a milky liquid in which the SiO2 and CO3 amorphous silicic acid and the crystalline calcium carbon- Contents are 8 grams and 4.95 grams per litre, l'eSPeCiVelY- ate which are presentinthe product are separate individual One litre of the milky liquid is placed in a three-neck grains. It is observed that the amorphous silicic acid is flask 0f glass and agitated at a Sllll'el' Speed 0f 18o-200 uniformly dispersed within the grains of calcium carbonreVOlUtOnS Per lnlnnle While being kept at Vallone ate of an average grain size of 0.05 micron. temperatures as specilied in Table 3 below. To this charge Example 4 are added a mixture of 144 cc. of an aqueous solution of 15% calcium chloride and 4 cc. of 28% aqueous ammonia An electro-magnetically stirred autoclave of a capacity under stirring and at a rate of 7.5 cc. per minute. The of 30 l. is charged with 15 l. of an aqueous solution of carbonation reaction takes place to form calcium 7% of calcium chloride which has contained 2 mols. of carbonate. The reaction is completed when the pH value ammonium hydroxide per mol. of the calcium chloride. of the reaction mixture has 'reached about 8.5-8.6. The To the charge are added slowly under stirring 900 grams crystalline reaction product deposited is removed from of sodium silicate ot a SiOZ/NazO molar ratio of 2.45 the reactor and washed with water until it is free from and of a SiO2 content of 40.3%, so that colloidal silicic the chloride ions. Drying at 100 C. for 3 hours gives a acid is deposited and there is formed an emulsion in composition of calcium carbonate having such properties which the CaClZ/SiOz molar ratio is 3.54. vNitrogen gas as shown in Table 3 below. For comparison, the above is then introduced into the reactor to a pressure of 7 process is repeated similarly except that sodium carbonate lig/cm?, and the charge is kept at 14 C. and agitated 40 is used in place of ammonium carbonate. The results are at a stirrer speed of 500 revolutions per minute. Carbon also shown in Table 3.

TABLE 3 Reaction condition and nature Carbonation reagent used ol'product Sodium carbonate Ammonium carbonate (the invention) (comparative) Reaction temperature in C 5-6 1748 29-30 5-6 17-18 Apparent dcuSityingJcc 0.567 0.541 0.732 0561..-.. 0.676.

Crystalline structure Vaterite plus 50% Vaterite plus Calcite... Calcite.

40% Calcite. 50% Calcite.

Grain size range,inmicrons 0.3-1.0 0.3-1.0 34 3-5 8-10.

dioxide gas is subsequently blown into the charge under The crystalline structure and grain vsize yrange are agitation and under a partial pressure of 0.3 lig/cm?. determined by X-ray ditfractometry and electron micro- The carbonation reaction takes place and is continued scope, respectively. until the pH value ot the reaction mixture has reached From the above test, it is seen that only the use of 8.4. The crystalline reaction product deposited is removed ammonium carbonate as the carbonation reagent results from the reactor and washed with water until it is free in the formation of the vaterite type crystalline calcium from the chloride ions. The product is then dried at 110 60 carbonate but the use of sodium carbonate leads to the C. for 18 hours in a through circulation drier and subformation of the calcite type crystalline calcium carbonate. sequently lightly ground to give-1 kg. of -very much comparan-ve Example 1 finely divided White powder of an apparent density of 0.38 g./cc. Electron microscopic observation .and X-ray 2 l. of distilled water are admrxed with various amounts diffractometry show that the powder is a composition in el SOfllnnl Sllleae haVlng a S102 Content 0f 2 7% and 3 which the amorphous silicic acid is uniformly dispersed SiOz/Naao nlnlfn' Talle 0f 3l as SP'eClllednn Table 4 in the grains of the vaterite type crystalline calcium carlJ'elOW- Tlle adl'nlXnfe 1S then added Wlln a milk 0f Slaled -bonate of a grain size range of 0.5-0.1 micron. lime Wlllh has been PTePeIed by InlXlng 89 grams 0f commercial slaked l1me w1th 400 ml. of Water thoroughly.

Example 5 70 The resulting liquid mixture is placed in a vessel and the An electro-magnetically stirred autoclave of a capacity vessel is further placed in a tanlr which is maintained at of 5 l. is charged with a milky liquid which consists of about 18 C. While the liquid mixture 1s kept at temperaa mixture of 3 l. of an aqueous solution of 4.5% of tures as specied in Table 4 below, a gaseous mlxture of calcium chloride and 375 grams of sodium silicate having 830 Inh/min. of carbon dioxide and 334 ml./min. of air a SiO2 content of 32.6% and a SiO2/Na20 molar ratio 75 is blown thereinto under agitation. As the carbonation 12 charge under agitation until the pH value of the reaction mixture has reached. 8.6. The reaction product deposited is removed, washed thoroughly with water and dried at 150 C. in a through circulation drier.

Y Sample No; 2.-A 30 1. autoclave is charged with 1.53

kg. .of the above mentioned sodium silicate, with 9 1. of water and with 5.97 l. of the above mentioned calcium chloride solution. The subsequent treatment is carriedV out in the same manner as in the above.

TABLE 4 Reaction condition and nature oi product 1st run 2nd run 3rd run Amount of sodium silicate added, in grams 48 48 120. Reaction temperature in C 19-20. 21., 21-22 Reaction time in minutes 70 120. 180. Apparent density 0.54 0.5 0.43. Crystalline structure (Xray dractometry) Calcite Calcite Calcite. Grain size range, in microns (electron micro- 1-2 3-4 in rod- 5'7 in rodscope determination). shaped. shaped.

In the following examples, various llers are tested for their reinforcing eiects 'for synthetic rubbers. The compositions and natures of the llers tested are tabulated in Table 5 below.

SampleNo. 3.-A l. autoclave is charged V.with 1.93 kg. of the above mentioned sodium silicate, With`11.3 1.

of water and with 3.75 1. of the above mentioned'calcium TABLE 5 Apparent Average Electron Fillers tested density pH grain Composition and characteristics micro- (gJcc.) size, in photograph Y microns @(100,000)

Sample No. 1 0. 38-0. 41 8.5 ca. 0.05 Uiifgrn composition of 1: 1 silicic acid/vaterite Fig. 4.

a 3. Sample No. 2 0. L12-0.44 8. 5 ca. 0.05 Uiifn composition of 1:2 silicio acidlvaterite Fig. 5.

a. Sample No; 3 0. 45-0. 46 8.5 0.1 Ucnifin .composition ofv 1:3 silicio acid/vaterite Fig.l 6.

2. 3. Commercial nely divided calcium carbonate (A) 0.35 10.0 ca. 0.05 Carbonates containing 32:18 CaO/MgO, surface Fig. 7.

treated Withiresinous acid, calcite CaCO3. 0. 67 8. 5 ca. 0.05 Calcite CaCOasurface-treated with ca. 2% oiiatty Fig. 8.

Commercial lnely divided calcium carbonate (B)..

acid.

vand with 5.941. of an Yaqueous-solutionk of 16.74%ca1cium chloride'which; has contained 2.1 mols. of ammonia per mol; of the calcium chloride.Nitrogen.gasisV introduced into the reactor to a pressure of 5`kg./cm.2, and-the charge is kept ata temperature of not higher than 10 C. and agitated. Carbon dioxide gas is then blown into the chloride solution. The subsequent treatment is Ycarried '40 out in the same manner as in the above.

Example V7 Various amounts of fillers tabulated in Table 5 are incorporated into a synthetic styrene/butadiene rubber (SBR) by means of 6 X 12." rolls. The resulting compositions are tested for the extending eiect. The test is performed on the test strips which have been prepared by pressing and vulcanizing sheets of mixtures comprising varying quantities ,of such ingredients as described in V Table 6 below, at 145 C. and under a pressure of 150 lig/cm.2 for a given period of time.

TABLE 6 Ingredients in the mixtures Sample No. 1 Sample No. 3 .Commercial nely divided calcium carbonate (B) SBR No. 1502, in parts by Weight 100 100 100 100 100 100V 100 100 100 Filler in parts by weight 120 160 80 120 160 80 120 160 Zinc oxide in parts by weight. 5 5 5 5 5 5 5 5 5 Stearic acid in parts by weight.. 3 3 3 3 3 3 3 3 3 Sulfur in parts by Weight 2 -2 2 .2 2 2 2 2 2 Nocceler D in parts by Weight-. 0. 5 0. 5 0.5 0.5 0. 5 0. 5 0.5 0.5 0. 5 Nocceler DM in parts by weight 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 .1. 5 l1. 0 1; 5 CHA in partslby Weight 0. 4 0. 6 0. 8 DEG in parts by weight 0. 24 0. 36 0:48

TABLE 7 Vulcan- Properties oi the vulcanised ization Sample No. 1 Sample No. 3 Commercial finely divided compositions time calcium carbonate (B) Tensile strength (kg/cm.l 20 110 108 110 91 97 102 69 72 69 30 109 111 112 93 100 107 59 68 66 300% modulus (kg./cm.2) 20 30 55 73 14 21 58 18 20 45 30 37 59 81 20 23 64 21 21 4o -Elongation (percent)- 20 720 670 510 850 800 600 590 590 570 y 30 640 520 450 700 750 580 540 570 570 Tear strength (Akg./cm.)- 20 31 34 37 25 33 37 21 21 21 30 30 35 39 23 34 38 21 20 22 Hardness (JIO') "0 53 (x3 7G 51 53 74 57 5S (,1 30 60 e8 78 53 60 75 57 60 b2 As will be seen from Table 7, the vulcanised compositions comprising SBR and the Sample No. l or the Sample No. 3 have higher tensile strength, higher modulus and higher tear strength than those comprising the commercial nely divided calcium carbonate and that the former have the elongation and hardness as high as the latter and show much excellent rubbery nature.

Example 8 Various amounts of fillers tabulated in Table 5 are incorporated into a synthetic acrylonitrile/ butadiene rubber (NBR) by means of 6 x 12 rolls. The resulting compositions are tested for the extending effect. The test 14 It is apparent that the use of the Samples Nos. 1 and 2 as the extender is advantageous over the use of the commercial calcium carbonates.

Example 9 TABLE 8 Ingredients in the mixtures Sample No 1 Sample N o. 2 Commercial finely divid- Commercial finely divided ed calcium carbonate (A) calcium carbonate (B) Hycar 1042, in parts 100 100 100 100 100 100 100 100 100 100 100 100 Filler in paxts 80 120 160 80 120 160 80 120 160 80 120 160 Zinc Oxide in part 5 5 5 5 5 5 5 5 5 5 5 5 Stean'c acid in part 3 3 3 3 3 3 3 3 3 3 3 3 Sulfur in parts.- 2 2 2 2 2 2 2 2 2 2 2 2 Accel CZ in part 1. 5 1. 5 1. 5 1. 1. 5 1. 5 Accel TMT in part 0. 1 0- 1 0. 1 0. 0. l 0. 1 Nocceler D in parts 0. 5 0. 5 0. 5 0. 5 0. 5 0. 5 Nocceler DM in parts 1. 5 1. 5 l. 5 1. 5 1. 5 1. 5 DEGin parts 0.4 0.6 0.8 0.32 0.48 0. 64

TABLE 9 Vulcan- Commercial nely dvid- Commercial finely divid- Properties o the vulcanised compositions isa'tion Sample No. 1 Sample No. 2 ed calcium carbonate (A) ed calcium carbonate (B) une (min.)

Tensile strength (kg/cm?) 20 131 127 137 121 122 124 Q3 86 75 87 84 73 30 118 120 138 116` 117 121 87 78 67 69 73 68 300% Modulus (kg/cm.2 20 36 67 35 50 90 l2 20 23 16 17 22 30 44 76 45 55 99 14 19 25 17 18 25 Elongation (percent) 20 700 600 280 730 610 500 780 720 640 680 750 580 30 600 530 250 590 540 400 670 680 570 600 680 530 Tear strength (kg/cm.) 20 37 47 40 33 38 44 25 30 35 19 22 22 30 36 44 36 30 35 42 25 29 35 19 22 22 Hardness (J IS) 20 63 75 85 63 70 84 60 60 70 60 60 67 30 63 76 S7 66 74 86 61 62 72 6l 61 68 procedure and the vulcanisation conditions are the same as in Example 7.

As will be clear from Table 11, the vulcanised compositions comprising the Samples Nos. 1 and 2 have ten- TABLE 10 Commercial finely Ingredients in the Sample No. 1 Sample N o. 2 divided calcium mixtures carbonate (A) Ameripole CB 220, in parts 100 100 100 100 100 100 Filler, in parts 80 120 160 S0 120 160 Zinc oxide, in parts. 5 5 5 5 5 5 3 3 3 3 3 3 2 2 2 2 2 2 0.5 0.5 0.5 0.5 0.5 0.5 1.5 1.5 1.5 1.5 1.5 1.5 Acting B, in parts 0.8 1. 2 1 6 0.8 1. 2 1. 6

TABLE 11 Vulcan- Properties ofthe vulcanised isation Sample No. 1 Sample N o 3 Commercial calcium compositions time carbonate (B) Tensile strength (kg/cm!) 15 119 103 95 96 128 107 25 35 39 120 96 97 120 105 27 34 34 300% Modulus (kg/cm?) 15 40 63 82 42 62 75 24 27 31 30 45 65 98 40 66 76 25 29 3l Elongation (percent) 15 610 460 340 580 580 460 310 10 400 30 590 450 30D 600 540 470 340 70 350 Tear strength (kg/cm.) 15 28 37 39 31 26 24 14 18 20 30 32 34 38 33 30 25 15 18 21 r Hardness (IIS) 15 60 66 72 66 72 79 62 76 70 30 60 68 74 64 74 82 62 77 70 sile strength and modulus of several times higher than those comprising commercial nely divided calcium carbonate but retain proper degrees of elongation and hard- DESS.

Example 10 Various amounts of fillers tabulated in Table 5 are incorporated in a synthetic rubber low cis-polybutadiene (Dien NET-). The resulting compositions are tested on the extending elect. The test is performed on the test strips which have been prepared press-vulcaiiising sheets of mixtures comprising such ingredients as specified in l5 As will be clear from the above table, the filler according to the present invention, namely Samples Nos. l and 3 improve thetear strength of isoprene rubber as much as the commercial i'inely divided calcium carbonate,

Table l2 below, at 141 C. and under a pressure of 200 5 and it can impart to isoprene rubber higher tensile strength kg./crn.2 fora given period of time. aswell as a proper degree of elongation without involv- TABLE 12 Ingredients in the mixtures Sample No. 1 Sample No. 2 Commercial inely divided calcium carbonate (B) Dien NF-35, 1n parts 100 100 100 100 100 100 100 100 100 Filleninparts 60 80 100 60 80 100 60 80 100 Zinc oxide, lnparts- 5 5 5 5 5 5 5 5 5 Stearic acid, in parts 3 3 3 3 3 3 3 3 3 Sulfur, in parts- 2 2 2 2 2 2 2 2 2 Aece1CZ,inparts 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 Sun Circo Sol 2XH (made by Sun 5 5 5 5 5 5 5 5 5 TABLE 13 Vulcan- Vulcan- Properties ofthe vulcanised compositions isation Sample No. 1 Sample No. 2 isation Comercial nely dividedY time time calcium carbonate (B) (min.) (mim) Y Y fiensiie strength (kg/51112)-; 47 64 77 66 6s V71 30 30 34 ai 56 Y 70 Y37 S5 88 90 40 31' V35 37 300%Modn1us (kg/cm!) 45 26 29 65 48 Y Y 51 5s 30 Y21 20 22 Y 60 28 33 6s 55 60 70 40 21 22 23 Elongation (percent) k45 53()v 45D. 350 510 480 425 30 800 750 630 60 500 450 400 480 450 400 4o 750 650 700 Tear strength (kg/ern.) 45 25 31 38 30 38 40 30 19 21 25 00 27 35 35 33 42 45 40- 20 24 VY25v Hardness (JIS) 45 45 58 75 60 63 73 30 47 52 60 Y Y 60 4s 60Y 75 60 64 77 40 49 53 62 From Table 1-3, it is clear that vthe Samples Nos. 1 ing increase in the hardness. Consequently, the filler of and 2 have more excellent reinforcing eliect than the 35 the invention apparently has a reinforcing effect for isocommercial iinely divided calcium carbonate. With the prene rubber, yas seen also from Table 1l. It may be noted commercial finely divided calcium carbonate, the optimum that the Sample No. 3 having a higher content of the time for vulcanisation is said to be y301-40 minutes. Acvaterite type orystallinecalcium carbonate yleads to high- .cordingly, .the test strips have been vulcanized for the er improvement in the tensile strength and shows optimum periods of 30 `and 40 minutes when the com- 40 reinforcing eiect. From this example, it can be conmercial calcium carbonate Was used as the iller. rmed that the new filler according to the presentinven- Example 11 tion shows an excellent and unique reinforcing effect for steric synthetic rubbers. Various amounts of llers tabulated m Table 5 are in- Com amtive Exam le 2 corporated in Van'isoprenerubber (IR-305) by Ymeansrof 45 p p Y 6 X 12" rolls. The resulting compositions are tested for In order to prove that the reinforcing effect of the uni- K the extending effect. The test is performed on the test form composition of amorphous silicic acid and the strips which have been prepared by press-vulcanizing vaterite type crystalline calcium carbonate according to sheets of mixtures comprising such ingredients as specified the present invention is superior to that of such a simple Vin Table 14 below, at 145 C. and under a pressure of 50 mixture in which iine particles of amorphous silicic acid 2 Y. 1 kg./ cm. for a given period of time. aremerely admixed with nely dividedcalcium carbonate TABLE 14 AIngredients in the mixture Sample No. 1 Sample No. 2 Commercial finely divided l calcium carbonate (B) iii-305, in parts 100 100 100 100 100 100 100 100 100 100 100 100 Filler, inparts s0 100 120 160 s0 100 120 160 Y s0 100 120 160 Zinc orideinparts 5 5 5 5 5 5 5 5 5 5 Y 5 5 `Steai'ic acid, in parts 3 3 3 3 3 3 3 3 3 3 `3 V3 sniruninparus 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 accei CZ, in parts 1. 5 1. 5 1. 5 1. 5 1. 5 1.5 1. 5 1. 5 1. 5 1. 5 1. 5 1.5

TABLE 15 Propertles'oi the Vulcan Commercial finely yvulcanised.compositions sation Sample No. 1 Sample No. 3 divided calcium time carbonate (B) (min.) Tensile strength (kg/cm2) 20 112 99 100 96 130 127 121 107 73 73 71 62 30 V122 104 101 96 125 114 120 102 61 70 73 61 300% Moduius (kg./em.2) 20 24 30 36 .49 25 25 27 35 3i 31 30 26 30 25 29 32 48 24 23 27 34 28 29 2s 26 Elongation (percent) 20 750 700 650 580 800 800 800 750 550 500 530 550 30 800 780 700 600 S00 S00 300 780 500 500 `530 580 -Tear strength (kg/cm.) 20 26 24 25 32 2a 25 27 V45 29 26 25 24 30 26 25 26 31 26 24 26 35 29 24 24 24 Hardness 20 52 60 65 s0 52 55 53 75 55 59 62 62 30 52 6i 65 si 52 57 63 76 55 59 62 62 and therefore the former exist outside the grains of the latter, the following test is performed. 1n the test, finely divided crystalline calcium carbonate of the vaterite type and of a grain size range of 0.3-0.5 micron is rstly prepared and l kg. of this product is dispersed in 10 l. of Water. The resulting dispersion is then added with 957 grams of such a sodium silicate in which the 'S102 content is 32.7% and the SiO2/Na20 molar ratio 2.52. Carbon dioxide gas is then blown into the admixture while kept at a temperature of not higher than 10 C. Amorphous silicic acid is deposited around and on the grains of the calcium carbonate. This mixture comprising silicic acid and calcium carbonate is ltered E by Buchner funnel, Washed with Water and dried. This product is hereinafter called Sample No. X. Further, 1 kg. of the same grade of crystalline calcium carbonate of the vaterite type is dispersed in l. of Water and the dispersion is ladmixed with 315 grams of colloidal silicic acid under agitation to form a completely uniform mixture which is subsequently dehydrated by filtration and dried. The resultant product is hereinafter called Sample No. Y. Electron microscopic observation of these Samples Nos. X and Y show that these are mixtures of silicic acid and the Vaterite type crystalline calcium carbonate (the proportion of silicic acid to calcium carbonate is 1:2.35 by weight). These samples, Nos. X and Y, as Well as the aforesaid Samples Nos. 1 and 2, are incorporated into three kinds of synthetic rubber, that is, NBR, high cispolybutadiene and low cis-polybutadiene in such proportions as specied in Table 16 below, and the resulting compositions are tested. The results are shown in Table 17 below. It may be seen that the reinforcing effect of the Samples Nos. X and Y is inferior to that of the Samples Nos. 1 and 2.

What We claim is:

1. A process for preparing calcium carbonate crystals selected from the group consisting of the vaterite type, aragonite type and mixtures thereof, having dispersed therein amorphous silicic acid, which comprises the steps of:

(a) treating a mixture of an aqueous suspension of colloidal silicic acid and a solution of calcium chloride with ammonium hydroxide so that the pH is at least 8;

(b) treating said mixture of increased alkalinity with a carbonating reagent selected from the group consisting of gaseous carbon dioxide and ammonium carbonate; and

(c) maintaining the pH of the carbonated mixture at a value of at least 8 by the addition of further ammonium hydroxide thereto.

2. A process according to claim 1, in which said carbonatiug reagent is gaseous carbon dioxide and wherein said carbon dioxide is diluted with an inert gas.

3. A process according to claim 1, in which said mixture of increased alkalinity is carbonated at a temperature below 20 C. and the vaterite type of crystal is formed.

4. A process according to claim 1, in which said mixture of increased alkalinity is carbonated at `a temperature above C. and the aragonite type of crystal is formed.

5. A composition of matter as set forth in claim 1.

6. A composition of matter comprising: a mixture of synthetic rubber selected from the group consisting of styrene/butadiene, acrylonitrile/butadiene, cis-butadiene and isoprene and a filler consisting of the composition of matter of claim 1, said iiller being present in an amount of from to 120 parts by Weight per 100 parts of said rubber.

TABLE 16 Kinds of synthetic rubbers N BR (Hycar 1042) High cis-polybntadene Low cis-polybutadiene (N F-35) (Ameripole CB 220) Sample No. 1 No. 2 No. X No. Y No. 1 No. 2 No. X No. Y No. 1 No, 2 No. X No. Y Ingredients in the mixture:

synthetic rubber, in parts 10o 100 100 100 100 100 100 100 100 100 100 100 Filler, in parts 100 100 10o 10o 5o 5o 50 50 10o 100 100 10o Zinc oxide, in parts-.- 5 5 5 5 5 5 5 5 3 3 3 3 Steario acid, in part 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 suirur,inparts 2 2 2 2 2 2 2 2 2 2 2 2 Accel CZ, in arts 1. 5 l. 5 1.5 1. 5 1 1 1 1 0.6 0.6 O. 6 0. 6 Sun Circo So 2XH 5 5 5 5 Vuleanisation conditions Press-vulcamsed at 145 C. Press-vulcanised at 141 C. Press-vuleanised at 141 C.

under 200 kg./cm.2 under 200 kg./ cm.2 under 200 kgJcrn.2

TABLE 17 NB R High cis-polybutadiene Low cis-polybutadiene Properties of the Vulcan- Yulean- Vulcanvulcanised compositions isation Sample No. isat1on Sample N o. isation Sample No.

time time time (min.) 1 2 X Y (min.) 1 2 X Y (min.) 1 2 X Y Tensile strength (kg.lcm.2)-- 2o 138 128 86 102 30 78 52 42 47 50 87 76 5o 60 3o 132 126 84 104 40 78 59 4o 52 6o 85 80 53 68 300% M0du1ns(kg./em.2) 20 36 38 58 37 30 25 24 20 19 50 6s 6o 5a 3o 44 45 72 43 40 24 24 2o 18 60 69 61 57 Elongation (percent) 20 750 700 500 800 30 830 750 730 780 50 400 400 230 350 30 600 630 480 680 40 63o 700 750 800 50 480 400 200 330 Hardness (JIS) 20 75 74 75 72 30 45 48 45 49 5o 75 77 76 73 3o 77 78 78 75 40 46 48 47 50 60 75 77 76 76 As to the vulcanisation additives used in Examples References Cited 7-11 and Comparative Example 2, the following abbrevi- UNITED STATES PATENTS ations are ern lo ed:

P y 2,954,382 12/1960 Hau 23-66 TMT: Tetramethyl-thlllralil dlslllplllde 3,133,824 5/ 1964 Podschus 106-306 CZ: n-Cyclohexyl-benzothiazole dlsulnamide 3,179,493 4 196 5 Diekmann 23 66 CHA: Cyclohexylamine DEG: Diethylene glycol IULIUS FROME, Primary Examiner.

Nocceler D and Nocceler DM are trade names of diphenyl guanidine and dibenzothiazyl sulphide, respec- MORRIS HERMAN Exammer tively. S. L. FOX, Assistant Examiner. 

